The phenylnaphthol compound which is a phenylnaphthalene compound is useful as an intermediate product for the production of functional organic materials such as medicines and dyes. For example, the indenonaphthopyran compound which is a photochromic coloring matter is synthesized from the indenonaphthol compound. So far, the indenonaphthol compound has been produced by using a benzophenone compound as a starting material.
According to the conventional method of producing the indenonaphthol compounds from the benzophenone compounds, it was necessary to produce the phenylnaphthol compounds having, on the naphthalene ring thereof, a substituent that is to be converted into an indeno group. Thus, the phenylnaphthol compounds have heretofore been synthesized from the benzophenone compounds through the reactions of a multiplicity of stages. Therefore, the production steps were complex, yields were poor and, as a result, the production cost was high, and improvements have been urged. Specifically, if a benzophenone compound having an asymmetrical molecular structure is used as the starting material, there are formed structural isomers, the phenylnaphthol compound is obtained in a greatly decreased yield, and improvements have been urged (e.g., see patent documents 1 and 2).
If it is attempted to synthesize a benzophenone compound represented by the following formula:
by the Friedel-Craft' s acylation reaction, selectivity of the positions to be acylated is so low that it is difficult to obtain the desired product in a high yield. Therefore the benzophenone compound had to be synthesized through a multiplicity of stages without relying on the Friedel-Craft' s acylation reaction.
Further, if the indenonaphthol compound is synthesized by using the known phenylnaphthol compound, a severe acidic condition is often required for condensing and cyclizing the naphthalene ring with the indene ring. Therefore, the object product is often decomposed and impurities are, in many cases, by-produced.
Described below is an example of synthesizing the indenonaphthol compound by using the conventional phenylnaphthol compound.

According to the conventional method as will be learned from the above example, very many steps were necessary before the phenylnaphthol compound was synthesized. Further, even if the indenonaphthol compound was to be synthesized from the conventional phenylnaphthol compound, problems remained in regard to decomposition of the object material and formation of impurities.